We constantly make decisions. Some seem simple: I booked dinner at a new restaurant, but I’m hungry now. Should I grab a snack and risk losing my appetite or wait until later for a satisfying meal—in other words, what choice is likely more rewarding?
Dopamine neurons inside the brain track these decisions and their outcomes. If you regret a choice, you’ll likely make a different one next time. This is called reinforcement learning, and it helps the brain continuously adjust to change. It also powers a family of AI algorithms that learn from successes and mistakes like humans do.
But reward isn’t all or nothing. Did my choice make me ecstatic, or just a little happier? Was the wait worth it?
This week, researchers at the Champalimaud Foundation, Harvard University, and other institutions said they’ve discovered a previously hidden universe of dopamine signaling in the brain. After recording the activity of single dopamine neurons as mice learned a new task, the teams found the cells don’t simply track rewards. They also keep tabs on when a reward came and how big it was—essentially building a mental map of near-term and far-future reward possibilities.
“Previous studies usually just averaged the activity across neurons and looked at that average,” said study author Margarida Sousa in a press release. “But we wanted to capture the full diversity across the population—to see how individual neurons might specialize and contribute to a broader, collective representation.”
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